Mechanical tree harvesters are used for logging trees. They typically consist of a tractor equipped with a boom. A grapple on the end of the boom grips a standing tree. A chain saw located below the grapple and controlled by the operator from the cab of the tractor, severs the tree. The operator maneuvers the boom and grapple to lay the severed tree on the ground and the process is repeated.
The guide bar is mounted on a pivot and the operator initially pivots the bar and chain to a protected position inside a channel of a rigid guard. With the tree held by the grapple, the guide bar and driven saw chain are pivoted out of the guard and through the base of the tree. In the process, the unguarded bar and chain will typically cut through the tree without incident and be returned to the protected position inside the guard prior to the operator maneuvering of the severed tree onto the ground.
The above refers to the normal operation. Not infrequently due to various circumstances that are encountered, the bar and chain are subject to damage. This may occur for example when trees are grouped too close together. A bar and chain will cut through the tree held by the grapple and begin cutting into a closely adjacent tree before the tree held by the grapple is completely severed. When the tree held by the grapple has been severed, the boom will instantly lift the tree. With the bar and chain embedded in the adjacent tree, this movement translates into a bending force applied to the bar. Something has to give which often results in the bar being bent and damaged.
In some cases, the tree trunk is so misshapen that the grapple will not firmly grip the tree. If the grapple loses its grip on the tree during the cutting operation, the tree will slide down against the bar and the bar will be damaged. Operator error is a further possibility. A lifting force is applied to prevent the kerf from collapsing and binding the chain. Too much lifting force applied during the cutting operation can cause the grapple to slide up the tree trunk and again a severe bending force is applied to the bar.
Other examples could be given but the common result of all these occurrences is that the bar becomes bent and most likely damaged. Bending occurs most frequently adjacent the juncture of the mounting bracket at the inner end of the bar. The bend is most often a sharp bend which invariably cracks the bar and renders it non-repairable. Such breakage of the guide bar is a ma]or concern and expense to the mechanical tree harvesting operation and alleviating the problem is an object of the present invention.